According to the prior art, the articles of the above reminded type are generally obtained by starting from two half-shells which are mechanically assembled by soldering or adhesive-bonding, with the hollow space defined inside the two half-shells being subsequently filled with foamed polyurethane.
According to another technique, disclosed in Italian patent application No. 21,815 A/87, a hollow case of thermoplastic polymer is formed by blow-molding, and said hollow case is then filled with a reactive polyurethanic mixture, which is then foamed.
Foamed polyurethane, used as the heat-insulating material in both of the above-described techniques, is obtained by starting from a formulation which is constituted by an organic diisocyanate, a polyol, a silicone surfactant, a polymerization catalyst and a foaming agent belonging to the class of chlorofluoroalkanes, such as Freon.
At present, the adoption of foamed polyurethane as a heat-insulating material causes problems of environmental character, in that the foaming agents of chlorofluoroalkane nature, such as Freon, are regarded as one among the main causes of alteration and destruction of the ozone layer existing in the stratosphere.
Unfortunately, replacing polyurethane with an equivalent material is a problem not easy to be solved, in that this polymer, by being foamed in situ according to the well-known R.I.M. (Reaction Injection Moulding) technique, makes it possible that rigid, self-supporting structural elements can be obtained even if the outer case is made from a thermoplastic polymer, and not from a metal sheet.
This outcome is due to the fact that polyurethane, by reacting in situ, perfectly adheres to the inner walls of the case, forming one single structural body with them.
The present Applicant has found now a process which makes it possible for heat-insulating structural elements to be obtained by using foamed thermopastic materials which do not require the use of chlorofluorocarbons as the foaming agents, and which, compared to the products according to the prior art, secure equal or better insulating characteristics --with their thickness being the same--simultaneously enabling the relevant technologies of production at the industrial level to be kept nearly unchanged.